Pyridaben, a newly developed pesticide, is widely used for the control of mites and insects. Like rotenone and fenazaquin, pyridaben acts by inhibiting NADHubiquinone oxidoreductase activity (complex I) (EC I.6.99.3) of the mitochondrial electron transport chain. The inhibition site has not been characterized. Knowledge of complex I with at least forty protein subunits is expanding rapidly as to structure and function, especially after it became clear that complex I is linked to several neurologic disorders including Parkinson's and Huntington's diseases and the aging process. To understand the structure of the pyridaben-inhibition site(s), we developed a photoaffinity probe that has the same inhibiting activity as pyridaben and the advantage of having a photoactiveable group (the trifluoromethyldiazirin). Tritium will be introduced into this ligand.